40 A NATURALIST IN MID-AFRICA. 



its present level.* Hence at this time most of 

 these countries would have been a series of islands 

 something like the present Sesse archipelago. 

 During the time that it remained at this level, 

 the rain washing down the sides of the hills tilled 

 the hollows between them with a flat deposit 

 of alluvial matter, giving the characteristic long, 

 broad, rlat valley bottoms found on all the present 

 rivers which enter the Nyanza. 



Then, either by the cutting away of a rock 

 barrier at the present Bipon falls, or by the forma- 

 tion of the Somerset Nile itself (for I fancy that 

 some authorities suppose that the original outlet 

 of the Victoria Nyanza was towards the north- 

 east), the lake began gradually to sink. It ap- 

 pears to have remained stationary about 40 feet 

 above its present level for a considerable time ; at 

 least there is at Tsimbande hill, near the Kagera, 

 a very marked terrace which makes me think so. 

 After this, it continued gradually to sink, and is 

 still falling. 



The effect of this process is curiously visible all 

 along the course of the Kagera, and even as far as 

 Urundi. One finds at fully '200 miles distance 

 from the Nyanza those long, flat, and dry 

 valleys, rilled with the rich neutral-tinted alluvium 

 that is common in Lower Egypt. As such a valley 

 gradually dries up, the Papyrus swamps which 



- ;: This I give from my observations of the height of the 

 alluvial deposit in Usoga and Kavirondo. 



